This invention relates to an electronic part mounting system for a printed circuit board for automatically mounting electronic parts on the printed circuit board.
In order to automatically mount electronic parts on a printed circuit board, the center of the mounting position must be determined on the printed circuit board. A pair of patterns are formed at every mounting position (hereinbelow termed as "a land") of each electronic part on the printed circuit board so as to decide the center of the mounting position.
FIG. 1 shows a prior-art printed circuit board, in which numeral 1 denotes a printed circuit board, numeral 2 denotes lands, numeral 3 denotes patterns, and numeral 4 denotes openings for fastening at a fixed position the printed circuit board. The hatched portions of the lands designate the portions on which the lead wires of electronic parts are to be placed and then electrically connected.
FIG. 2 is an explanatory view showing a prior-art mounting system. Referring to FIG. 2, numeral 5 denotes conveyor belts for carrying the printed circuit board 1 along a guide rail (not shown). The belts are stopped by the operation of an elevational movement type limit switch 6 when the printed circuit board arrives at a predetermined position. Then, elevational movement type projecting rods 7 are projected into the openings of the printed circuit board to fasten the circuit board. Numeral 8 denotes a mounting controller, numeral 9 denotes a pattern recognition camera, numeral 10 denotes an electronic part recognition camera, numeral 11 denotes an attracting head for attracting an electronic part or component 13, and numeral 12 denotes a case for containing the electronic part or component 13. The pattern recognition camera 9 and the attracting head are fastened to one another. X-axis, Y-axis and Z-axis illustrated in the drawing are imaginary coordinate axes set in the mounting controller 8. The coordinate axes are used to move the pattern recognition camera 9 and the attracting head 11 to predetermined coordinate positions.
FIG. 4 is a flowchart for explaining the operating steps of the prior-art mounting system illustrated in FIG. 2, in which numerals 41 to 45 denote the operating steps. More specifically, the pattern recognition camera 9 is operated by the mounting controller 8 in FIG. 2 to read out a pair of patterns 3 provided at both sides of the lands 2 (in step 41). The central position of the land is calculated by calculating means (not shown) in the mounting controller (in step 42). Then, the mounting controller moves the attracting head 11 to pick up one electronic part 13 from the case 12, moves the electronic part recognition camera 10, and allows the camera 10 to recognize the electronic part 13 (in step 43). Next, the central position of the electronic part is calculated by the calculating means in the mounting controller (in step 44). Finally, the mounting controller moves the attracting head 11 to a predetermined land and places the electronic part on the land when the central position of the land coincides with that of the electronic part (in step 45). Thus, the lead wires of the electronic part are placed on predetermined positions of the land (the hatched portions of the land in FIG. 2 which are coated in advance with an adhesive material), and electrically bonded in the next step.
The operations of mounting the electronic parts as described above are sequentially executed each time on electronic part is to be mounted.
FIGS. 3(a), 3(b) and 3(c) are perspective views of a printed circuit board 1 for showing a problem associated therewith. More particularly, the printed circuit board has a small deformation in the longitudinal direction. The figures illustrate the types of the deformations in an enlarged manner. Since the printed circuit board has these deformations, the stopping position of the printed circuit board is slightly at an error. As illustrated in FIG. 1, the pair of patterns 3 must be provided for each land 2. Thus, it is necessary in the prior-art system to provide the step of reading out the pattern for each land when mounting the electronic part. The mounting process has such drawbacks as a long time requirement for mounting the components, thereby reducing the system's efficiency.